The invention is directed to a method and apparatus for storing images on a mass memory device such as a disk storage module for subsequent printing on a high-speed copier or printer. More particularly, the method and apparatus are directed to controlling disk accesses for image loads and retrieves such that the disk storage is preferably available to retrieve or output images from the disk storage module whenever the images are needed for printing.
High-speed digital copiers and printers require temporary storage for images prior to printing them. Typically, a printer apparatus will include an image storage subsystem for storing image data representing the images. This image storage subsystem serves two important purposes. First, it decouples the speed at which input images are acquired (scanned or rasterized) from the speed at which they are printed. Second, the temporary storage allows multiple copies of a document to be produced without having to re-acquire the input images; i.e., rescan the document or in the case of an input from a computer rerasterize the data from a coded form or object form used in a page description language. For high-volume printing, where multiple sets of large documents need to be produced, the temporary storage is most economically implemented using one or more disk drives or hard drives. Compressing the images before they are stored on the disks can further increase the capacity of the temporary storage.
A system using a disk memory to store images prior to printing them is disclosed in U.S. Pat. No. 5,848,226 to Chen et al. Chen et al discloses a high-speed digital printing system that can output over 100 page-size images per minute. A disk memory stores information in compressed form for output to an image out terminal (IOT) or marking engine as needed. A typical letter-sized page image at 600 dots per inch resolution may require 4 Megabytes of data to be furnished to the marking engine or IOT. Such image data may be required to be accessed from disk memory within a period of 300 milliseconds. In addition, there are other demands of storing image data in the disk memory for recording on subsequent image frames. Data input to the system may be derived from word processors or other sources of electronic image information and typically are expressed in a page description language such as HP-PCL or Postscript(trademark) and require decomposition such as through rasterization. Image data may also be input to the system from a scanner which provides rasterized information. The decomposed or rasterized image data may then be subject to compression to reduce storage requirements and be stored in the disk memory.
Chen et al notes the problem of competition for bandwidth in submitting data to the image output terminal (IOT) and competition in retaining a usable supply of image data to be delivered to the JOT when needed.
Chen et al resolves the problem of competition for disk access by providing a priority between software entities that provide commands to an operating system. In Chen et al requests from the marking engine for image data are assigned a highest priority so that decomposed data may be taken in real time without undergoing compression or may be retrieved from the disk ahead of other prior requests that are of less priority.
A problem with the system of Chen et al is that when a lower priority request is being operated upon, the higher priority request must wait until completion of the lower priority request and thus requires a skip frame period to be introduced which can affect adversely upon productivity.
It is therefore an object of the invention to provide an improved method and apparatus having a more optimum control over disk or mass memory access to improve productivity of the marking engine.
In accordance with a first aspect of the invention, there is provided a printer apparatus comprising a marking engine subsystem for recording information on an image recording member; and an image storage subsystem for buffering image data for output to the marking engine subsystem, the image storage subsystem including (a) an input for receiving rasterized image data; (b) a data compressor that operates on the rasterized image data to compress the rasterized image data to form compressed image data; (c) a disk storage module that is operable to receive, store and output the compressed image data; (d) a semiconductor RAM memory device that stores at least one page of the compressed image data; (e) a data decompressor that operates on the compressed image data output by the RAM memory device and decompresses the compressed image data to decompressed rasterized image data form for output to the marking engine subsystem; and (f) a controller that determines if the disk storage module is ready to operate in a write mode to receive compressed image data currently being stored in the RAM memory device and determines if the disk storage module is ready to operate in a read mode to output compressed image data from the disk storage module for transfer to the RAM memory device and, if the disk storage module is ready to operate in both modes, the controller is operative to provide a preference for operation of the read mode and controls the disk storage module so that compressed image data is output from the disk storage module and written into the RAM memory device.
In accordance with another aspect of the invention, there is provided in a printer apparatus that includes a marking engine subsystem for recording information on an image recording member an image storage subsystem for buffering image data for output to the marking engine subsystem, the image storage subsystem comprising a disk storage module that is operable to receive, store and output image data; and a controller that determines if the disk storage module is ready to operate in a write mode to receive image data and determines if the disk storage module is ready to operate in a read mode to output image data from the disk storage module, and if the disk storage module is ready to operate in both modes, the controller is operative to provide a preference to the read mode and image data is output from the disk storage for subsequent output to the marking engine subsystem; and wherein the controller controls operation of the write mode so that transfers of image data to the disk storage module are limited to no more than a portion of the image data of a page before permitting operation of the read mode.
In accordance with yet another aspect of the invention, there is provided a method of managing movement and storage of image data to and from a mass memory device in a printer apparatus, the method comprising determining if the mass memory device is ready to operate in a write mode to receive image data; determining if the mass memory device is ready to operate in a read mode to output image data stored in the mass memory device; and if the mass memory device is ready to operate in both modes: a) providing preference for operation in the read mode, and b) outputting from the mass memory device image data stored in the mass memory device; and c) controlling an operation of the write mode so that transfers of image data to the mass memory device are limited to no more than a portion of the image data of a page.
In accordance with still another aspect of the invention, there is provided a method of managing movement of image data in a printer apparatus comprising (a) inputting rasterized image data to an image storage subsystem of the apparatus; (b) compressing the rasterized image data to compress the rasterized image data to form compressed image data; (c) storing at least one page of the compressed data in a semiconductor RAM memory device; (d) outputting the compressed data from the RAM memory device to a disk storage module; (e) outputting the compressed image data from the disk storage module to the RAM memory device; (f) outputting the compressed image data from the RAM memory device that was previously stored in the disk storage device to a data decompressor; (g) decompressing the compressed image data to decompressed rasterized image data form; and (h) determining if the disk storage module is ready to operate in a write mode to receive transfers of compressed image data currently being stored in the RAM memory device and determining if the disk storage module is ready to operate in a read mode to output compressed image data from the disk storage module for transfer to the RAM memory device and, if the disk storage module is ready to operate in both modes, preference is provided for operation in the read mode and compressed image data is output from the disk storage module and written into the RAM memory device.
In accordance with still another aspect of the invention, there is provided a method of managing movement and storage of image data to and from a mass memory device in a printer apparatus, the method comprising determining when a next retrieval request is expected for transferring image data from the mass memory device in a read mode; and controlling transfers of image data to the disk storage module so that in a write mode, the transfers are limited to no more than a portion of the image data of a page and the amount of image data transferred in the write mode is related to time remaining until the next expected retrieval request.